In medium saucepan, bring cream, milk, sugar and 1 pinch salt to simmer, whisking just until sugar is dissolved. Remove from heat, stir in mint stems and let steep, 15 minutes. Transfer to bowl and let cool completely in ice water bath; cover and refrigerate for 2 hours or overnight. Strain mixture into chilled bowl of ice cream maker and process according to manufacturer's directions; fold in chocolate. Serve garnished with mint springs.